Fix blur noise effect using incorrect scaling value
QGuiApplication::primaryScreen()->logicalDotsPerInch() sometimes reports incorrect scale value, for example 95.951 (or even lower) instead of 96.0 at 1x scale and this caused to simply darken blurred areas instead of noising them.
This patch sets a minimum 1x scale for the noise texture, because realistically we will never be below that.
Reviewed By: davidedmundson
Subscribers: davidedmundson, kwin, KWin
Differential Revision: https://phabricator.kde.org/D12519